Transport Barrier "creates ozone hole

Researchers are investigating processes in the ozone hole that is developing

Antarctic ozone hole in October 2005 NASA
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Atmospheric researchers have discovered a phenomenon that contributes significantly to the early formation of the ozone hole: In the polar vortex - where the ozone hole over the Antarctic is formed every winter - a double transport barrier builds up. It prevents the exchange of air between the ozone-rich ambient air and the ozone-depleted layer inside the vortex. Nitrogen also plays an important role in this process, as the researchers report in the Journal of Geophysical Research.

"With the help of climate models, the future of the ozone hole can only be reliably predicted if processes such as the formation of the ozone hole are correctly understood, " explains Simone Tilmes, who evaluated the scientific data at Forschungszentrum Jülich and now at the renowned National Center for Atmospheric Research in Boulder, USA researches.

In the winter, the well-known ozone hole in the stratosphere forms regularly in the Antarctic. Here, during the winter months, the so-called polar vortex revolves around twenty kilometers. In these very cold air masses isolated from the environment by strong wind currents, all ozone is destroyed in a wide range every winter. "The human-induced stress on the stratosphere with chlorine compounds is now clearly identified as the cause of the ozone hole, " explains Rolf Müller from Forschungszentrum Jülich. "So far, however, we know very little about what happens in the Antarctic stratosphere in the fall just prior to the formation of the ozone hole."

Shielding stronger than expected

For the first time, data from a Japanese satellite experiment (ADEOS-II / ILAS-II: Advanced Earth Observing Satellite / Improved Limb Atmospheric Spectrometer) are available, which allow to study the conditions in the early phase of the forming ozone hole. Jülich scientists, together with their Japanese counterparts, were able to show that the air inside the polar vortex, even during vortex formation, is more shielded from the surrounding air layer than previously known.

The scientists discovered a double "transport barrier" at the edge and within the polar vortex, which ensures that there is no exchange between the polar vortex and the surrounding air masses. It causes the ozone loss to begin already in the early winter: The naturally occurring nitrogen in the stratosphere decomposes ozone at this early stage. The barrier in the polar vortex ensures that the now ozone-poor air can not exchange with the ozone-rich air masses outside the vortex. With decreasing temperatures in the polar vortex ice clouds form, where the known ozone depletion by chlorine radicals takes place. The ozone hole is created. display

Even more stable ozone hole in the future?

According to the researchers, a trend is already visible for future development: "The stratosphere continues to cool and in the polar vortex ever more cold records are broken, " says Rolf M ller. As a result, the polar vortexes become more stable and the exchange between ozone-rich and poor air layers is reduced. Whether climate change is already noticeable here, however, is still unclear.

(Forschungszentrum J lich, 22.12.2006 - NPO)